Aluminum inhibits the growth of hydroxyapatite crystals developed on a biomimetic methacrylic polymer

ProjectAluminum (Al) is an increasing problem in biomedicine since it can interact with phosphates. Bone is one of the preferential target tissues of Al deposition: Al interacts with mineralization and/or bone cell activities. We searched the influence of Al deposition in hydroxyapatite developed on a biomimetic polymer (carboxymethylated poly(2-hydroxyethyl-methacrylate)) which mimics bone mineralization in the absence of cells.ProceduresPellets of polymer were incubated for 5 days in a synthetic body fluid (SBF) to induce mineralization, then 21 days in SBF containing 20, 40 and 60 μg/L Al³⁺. Other pellets were incubated in SBF containing commercial Al foil (33 mg/vial) either in 1, 2 or 6 pieces. The mineral deposits were dissolved in HCl and Ca²⁺, PO₄^3? and Al³⁺ content was measured. Hydroxyapatite was characterized by SEM and X energy-dispersive X-ray analysis (EDX).ResultsThe amount of Al³⁺ was dose-dependently increased in Ca/P deposits on the polymer pellets. At high concentration (or with the 6 Al foils) growth of hydroxyapatite calcospherite was inhibited; only calcified plates emerging from the polymer were observed. Pellets incubated with 1 and 2 Al foils exhibited a reduction in calcospherite diameter and an increase in the Al³⁺/Ca²⁺ ratio. EDX identified Al in the mineral deposits.ConclusionsIn this acellular model, Al³⁺ altered the growth of calcospherites at low concentration and inhibited their development at high concentration. In SBF, a release of Al³⁺ from aluminum foils also inhibited mineralization. This study emphasizes the importance of Al in bone pathology and stresses the question of its release from biomaterials.     

Oriented immobilization of proteins on hydroxyapatite surface using bifunctional bisphosphonates as linkers

Oriented immobilization of proteins is an important step in creating protein-based functional materials. In this study, a method was developed to orient proteins on hydroxyapatite (HA) surfaces, a widely used bone implant material, to improve protein bioactivity by employing enhanced green fluorescent protein (EGFP) and β-lactamase as model proteins. These proteins have a serine or threonine at their N-terminus that was oxidized with periodate to obtain a single aldehyde group at the same location, which can be used for the site-specific immobilization of the protein. The HA surface was modified with bifunctional hydrazine bisphosphonates (HBPs) of various length and lipophilicity. The number of functional groups on the HBP-modified HA surface, determined by a 2,4,6-trinitrobenzenesulfonic acid (TNBS) assay, was found to be 2.8 × 10(-5) mol/mg of HA and unaffected by the length of HBPs. The oxidized proteins were immobilized on the HBP-modified HA surface in an oriented manner through formation of a hydrazone bond. The relative protein immobilization amounts through various HBPs were determined by fluorescence and bicinchoninic acid (BCA) assay and showed no significant effect by length and lipophilicity of HBPs. The relative amount of HBP-immobilized EGFP was found to be 10-15 fold that of adsorbed EGFP, whereas the relative amount of β-lactamase immobilized through HBPs (2, 3, 4, 6, and 7) was not significantly different than adsorbed β-lactamase. The enzymatic activity of HBP-immobilized β-lactamase was measured with cefazolin as substrate, and it was found that the catalytic efficiency of HBP-immobilized β-lactamase improved 2-5 fold over adsorbed β-lactamase. The results obtained demonstrate the feasibility of our oriented immobilization approach and showed an increased activity of the oriented proteins in comparison with adsorbed proteins on the same hydroxyapatite surface matrix.     

Modeling the interaction of seven bisphosphonates with the hydroxyapatite(100) face

The interaction of seven pamidronate bisphosphonate (Pami-BPs) and its analogs with the hydroxyapatite (HAP) (100) surface was studied using density functional theory (DFT) and molecular dynamic (MD) methods. Partial Mulliken oxygen atomic charges in protonated structures were calculated at the level of B3LYP/6-31G*. The MD simulation was performed using the Discover module of Material Studio by compass force field. The results indicate the abilities of donating electrons of the oxygen atoms of the phosphate groups that are closely associated with the antiresorptive potency. The binding energies, including vdw and electrostatic, are used to discuss the mechanism of antiresorption. The results of calculations show that the strength of interaction of the HAP (100) face with the bisphosphonates is N(4)?>?N(6)?>?N(7)?>?N(5)?>?N(3)?>?N(2)?>?N(1) according to their experimental pIC(50) values.     

Systematic fabrication of nano-carbonated hydroxyapatite/collagen composites for biomimetic bone grafts

A novel biomimetic self-assembly method was designed to create nano-carbonated hydroxyapatite/collagen (nCHAC) composites by means of incorporating various collagen and carbonate concentrations using solutions such as CaCl(2), H(3)PO(4), and Na(2)CO(3). At a given range of collagen and carbonate content, the nanosized inorganic phase of the newly synthesized material has a low degree of crystallinity which resembles that of natural bone. By manipulating the concentrations of collagen and carbonates, various morphologies of the nCHAC can be obtained. The crystal size of nCHAC is dependent on the concentration of carbonate and collagen present in the composites. For instance, higher collagen concentration results in smaller crystal nCHAC crystal size. Conversely, the higher the carbonate content, the smaller are the crystal size and the collagen fibril assembly. As the carbonate content increased, the plate-like crystals first became needle-like structures, subsequently short needle-like crystals and eventually became spherical particles. From this study, our method showcased the flexibility of fabricating various types of nCHAC composites which can be designed for different bone applications.     

In vitro and in vivo tests of hydrothermally synthesised hydroxyapatite coating

High pure and crystalline Hydroxyapatite (HA) coatings on titanium alloy were prepared by hydrothermal synthesis (HS) of plasma-sprayed (PS) precursors from brushite powders (HS-HA). In vitro and in vivo tests were done to evaluate its biological property. The HS-HA coating was compared with the current PS-HA coating. Cultures of the primary osteoblasts on these two HA coatings showed similar cell attachment, proliferation and alkaline phosphatase (ALP) expression. The cell morphology on the coatings was demonstrated by scanning electron microscopy (SEM). The cell spread well at 1 day after seeding culture and the extracellular matrix was secreted after 14 days culture. Histomorphometric analysis was conducted on samples implanted in femoral bone of four dogs for 1 and 3 months, and bone-implant contact percentage was evaluated by light microscopy. The calcium and phosphate distribution on the interface of bone-implant was analysed by SEM and electron dispersive X-ray (EDX) analysis. The results show the osteoconduction of HS-HA coated implants.     

Behavior of osteoblasts on the surfaces of nanocrystalline hydroxyapatite coating

Background  

The aim of this study was to investigate the effect of nanocrystalline hydroxyapatite (HA) coatings on the activity of osteoblasts.     

Nano-silver-incorporated biomimetic polydopamine coating on a thermoplastic polyurethane porous nanocomposite as an efficient antibacterial wound dressing

Background

Developing an ideal wound dressing that meets the multiple demands of good biocompatibility, an appropriate porous structure, superior mechanical property and excellent antibacterial activity against drug-resistant bacteria is highly desirable for clinical wound care. Biocompatible thermoplastic polyurethane (TPU) membranes are promising candidates as a scaffold; however, their lack of a suitable porous structure and antibacterial activity has limited their application. Antibiotics are generally used for preventing bacterial infections, but the global emergence of drug-resistant bacteria continues to cause social concerns.

Results

Consequently, we prepared a flexible dressing based on a TPU membrane with a specific porous structure and then modified it with a biomimetic polydopamine coating to prepare in situ a nano-silver (NS)-based composite via a facile and eco-friendly approach. SEM images showed that the TPU/NS membranes were characterized by an ideal porous structure (pore size: ~?85 μm, porosity: ~?65%) that was decorated with nano-silver particles. ATR-FITR and XRD spectroscopy further confirmed the stepwise deposition of polydopamine and nano-silver. Water contact angle measurement indicated improved surface hydrophilicity after coating with polydopamine. Tensile testing demonstrated that the TPU/NS membranes had an acceptable mechanical strength and excellent flexibility. Subsequently, bacterial suspension assay, plate counting methods and Live/Dead staining assays demonstrated that the optimized TPU/NS2.5 membranes possessed excellent antibacterial activity against P. aeruginosa, E. coli, S. aureus and MRSA bacteria, while CCK8 testing, SEM observations and cell apoptosis assays demonstrated that they had no measurable cytotoxicity toward mammalian cells. Moreover, a steady and safe silver-releasing profile recorded by ICP-MS confirmed these results. Finally, by using a bacteria-infected (MRSA or P. aeruginosa) murine wound model, we found that TPU/NS2.5 membranes could prevent in vivo bacterial infections and promote wound healing via accelerating the re-epithelialization process, and these membranes had no obvious toxicity toward normal tissues.

Conclusion

Based on these results, the TPU/NS2.5 nanocomposite has great potential for the management of wounds, particularly for wounds caused by drug-resistant bacteria.

     

Effects of fibrin on the integration hydroxyapatite coating implants: experimental study in a rabbit model

The purpose of this study was to investigate the effects of the addition of fibrin (SAF) to titanium alloy implants coated with hydroxyapatite (HAP) on osteogenesis in rabbits. A titanium (Ti) alloy implant was inserted into the femoral neck of twenty-four adult rabbits. Six rabbits were included on each of the following groups: Ti control, HAP-coated Ti module, HAP-coated Ti module with added fibrin glue and Ti module also with added fibrin glue. After seven weeks, bone growth was examined radiographically and by histo-morphometry. The SAF/HAP mixture did caused to a significant increase in bone growth compared to the other groups. The addition of fibrin did not result in an increase in new-bone growth and increase the formation of fibrous tissue in contact with the implant. We concluded that SAF did not demonstrate osteoinductive properties.     

Antibacterial activation of hydroxyapatite (HA) with controlled porosity by different antibiotics

In order to prevent the increasing frequency of per-operative infections, bioceramics can be loaded with anti-bacterial agents, which will release with respect to their chemical characteristics. A novel hydroxyapatite (HA) was elaborated with specific internal porosities for using as a bone-bioactive antibiotic (ATB) carrier material. UV spectrophotometry and bacteria inhibition tests were performed for testing the ATB adsorption and the microbiological effectiveness after loading with different antibiotics. The impregnation time, ATB impregnating concentration, impregnation condition and other factors, which might influence the ATB loading effect, were studied by exposure to different releasing solvents and different pathogenic bacteria: Staphylococcus aureus, Staphylococcus epidermidis and Escherichia coli. It clearly showed that the facility of ATB loading on this porous HA is even possible just under simple non-vacuum impregnation conditions in a not-so-long impregnating interval. The results also showed that, for all three types of ATB (vancomycin, ciprofloxacin and gentamicin), adsorbed amount on the micro-porous HA were hugely higher than that on dense HA. The micro-porosity of test HA had also significantly prolonged the release time of antibiotics even under mimic physiological conditions. Furthermore, it also has primarily proved by a pilot test that the antibacterial efficiency of crude micro-porous HA could be further significantly improved by other methods of functionalization such as cold plasma technique.     

Synthesis and biological evaluation of a series of aromatic bisphosphonates

Geminal bisphosphonates display varied biological activity depending on the nature of the substituents on the central carbon atom. For example, the nitrogenous bisphosphonates zoledronate and risedronate inhibit the enzyme farnesyl diphosphate synthase while digeranyl bisphosphonate has been shown to inhibit the enzyme geranylgeranyl diphosphate synthase. We now have synthesized isoprenoid bisphosphonates where an aromatic ring has been used to replace one of the isoprenoid olefins in an isoprenoid bisphosphonate and investigated the ability of these new compounds to impair protein geranylgeranylation within cells. Several of these new compounds are potent inhibitors of the enzyme geranylgeranyl diphosphate synthase.     

Jumping robots: a biomimetic solution to locomotion across rough terrain

This paper introduces jumping robots as a means to traverse rough terrain; such terrain can pose problems for traditional wheeled, tracked and legged designs. The diversity of jumping mechanisms found in nature is explored to support the theory that jumping is a desirable ability for a robot locomotion system to incorporate, and then the size-related constraints are determined from first principles. A series of existing jumping robots are presented and their performance summarized. The authors present two new biologically inspired jumping robots, Jollbot and Glumper, both of which incorporate additional locomotion techniques of rolling and gliding respectively. Jollbot consists of metal hoop springs forming a 300 mm diameter sphere, and when jumping it raises its centre of gravity by 0.22 m and clears a height of 0.18 m. Glumper is of octahedral shape, with four 'legs' that each comprise two 500 mm lengths of CFRP tube articulating around torsion spring 'knees'. It is able to raise its centre of gravity by 1.60 m and clears a height of 1.17 m. The jumping performance of the jumping robot designs presented is discussed and compared against some specialized jumping animals. Specific power output is thought to be the performance-limiting factor for a jumping robot, which requires the maximization of the amount of energy that can be stored together with a minimization of mass. It is demonstrated that this can be achieved through optimization and careful materials selection.     

In vitro and in vivo bioactivity of CoBlast hydroxyapatite coating and the effect of impaction on its osteoconductivity

The novel non-thermal CoBlast process has been used recently to create a hydroxyapatite coating on metallic substrates with improved biological response compared to an uncoated implant. In this study, we compared the biological effect of coatings deposited by this process and the industrial standard technique - plasma-spray. Physicochemical properties of these two coatings have been found to be significantly different in that CoBlast HA is less rough but more hydrophilic than the plasma-spray HA as evidenced by data obtained from profilometry and goniometry. Mesenchymal stem cell attachment and adhesion are enhanced on CoBlast HA. Analysis by a combination of EDX and ICP suggests that the higher crystallinity retained by the CoBlast HA result in slower coating dissolution. Detailed in vitro evaluation reveals that plasma-spray HA might induce slightly faster cell proliferation and earlier osteogenic differentiation, but CoBlast HA becomes equivalent to it by the late osteogenic stage. PCR array facilitated the identification of differentially regulated genes involved in various functional aspects of in vitro osteogenesis by the CoBlast HA coating. The expression level of the functional protein products of these genes are in agreement with the PCR data. Coating metallic screws with HA significantly improves the in vivo osseointegration. By measuring of removal force using torque measurement instrument and analyzing the patterns found in X-ray images it is demonstrated that the two HA coatings elicit comparable osseointegration. Using simulated impaction model, CoBlast HA is shown to maintain better performance in cell attachment and mineralization than plasma-spray HA, especially following significant impactions. This might indicate a potentially greater osteoconductivity of CoBlast HA coating in shear-stress associated surgical applications. Collectively, it was demonstrated that CoBlast HA is an effective alternative to plasma-spray HA coating and a promising replacement for specialized surgical applications.     

Cadmium-mediated resistance to metals and antibiotics in a cyanobacterium

Summary Cadmium-resistant strains of the cyanobacterium Nostoc calcicola were isolated through the step-wise transfer of the organism to higher levels of the metal. One of the Cd-resistant strains (Cd^r–10) showed cross-resistance to antibiotics like neomycin (1 g/ml), chloramphenicol (3 g/ml) but not to streptomycin. The Cd-resistant strain also tolerated elevated levels of metals such as zinc (20 ppm) and mercury (1 ppm). The stability of the metal-resistance required the presence of Cd²⁺ ions in the growth medium. It is suggested that metal resistance may also be determined by gene(s) on the antibiotic resistance plasmids in cyanobacteria.     

Manipulating the bioactivity of hydroxyapatite nano-rods structured networks: Effects on mineral coating morphology and growth kinetic

Background

Nano-hydroxyapatite particles have better bioactivity than the coarse crystals. So, they can be utilized for engineered tissue implants with improved efficiency over other materials. The development of materials with specific bioactive characteristics is still under investigation.

Methods

The surface properties of four hydroxyapatite materials templated by different micelle-polymer structured network are studied. The synergistic interaction of each block copolymer in contact with CTAB rod-like micelles results in crystalline HAp nano-rods of 25–50 nm length organized in hierarchical structures with different micro-rough characteristics.

Results

It was observed that the material in vitro bioactivity strongly depends on the surface structure while in a minor extent on their Ca/P ratio. So, MIII and MIV materials with Skewness parameter R_sk > 2.62 favored the formation on their surfaces of net-like phase with a high growth kinetic constant; while MI and MII (R_sk ≤ 2.62) induced the appearance of spherulitic-like structures and a growth rate 1.75 times inferior. Material biocompatibility was confirmed by interaction with rat calvarial osteoblasts.

Conclusions

The different structures growth is attributed to a dissimilar matching of crystal planes in the material and the apatite layer formed. In specific synthesis conditions, a biocompatible material with a Ca/P ratio close to that for the trabecular bone and a morphology that are considered essential for bone-bonding was obtained.

General significance

The creation of implantable devices with a specific bioactive characteristic may be useful to manipulate the attachment of cells on mineral coating directly affecting the stability and life of the implant.     

Intramolecular catalysis of biomimetic Michael additions to cyclopentenones

A study of the Michael additon of n-propyl mercaptan to a series of cyclopentenones shows that intramolecular hydrogen bonding enhances the rate. The possible significance of this observation is discussed.